It is known when manufacturing structures from composite materials to apply heat, pressure, and vacuum. One technique for applying vacuum is known as vacuum bagging.
During vacuum bagging, a vacuum is applied over a period of time to a laminate consisting of a substrate and a resin. The created vacuum sucks excess resin, trapped air, volatiles, etc. out of the laminate, helping to create a laminate free of cavities and impurities which will eventually be cured so as to form the structure. In addition, the vacuum might also improve maintaining the laminate in an appropriate position for curing.
As shown in FIG. 1, a typical vacuum bagging operation begins by laying the laminate (1) inside a mold (7) having the form of the structure to be manufactured. Once the laminate (1) is secured in place, a layer of “consumable materials” is laid against the laminate. Consumable materials might be, for example, sheets of fabric or plastics that facilitate the vacuum bagging process. One such consumable material might be a release film (2), consisting of a layer of thin plastic, which is applied directly against the laminate (1) or, alternatively, on top of a peel ply (3). Another example of a consumable material might be a sheet of “breather” (4), which might be a nylon sheet that absorbs resin sucked out of the laminate (1). The breather (4) can be used to make the vacuum level uniform inside the vacuum bag (5), and the release film (2) can be used to control the amount of resin that will be sucked out of the laminate (1), thus preventing the breather (4) from being permanently bound to the laminate (1) during curing. Together, the release film (2) and breather (4) may improve the flow of resin sucked out of the laminate (1) and its collection.
Once the consumable materials are applied against the laminate (1), the mold or tool (7) to which vacuum will be applied is delimited and sealed by sealant tape (6). The vacuum bag (5), which might be a plastic sheet, such as nylon with a thickness in the range of about 0.002 to 0.003 inches, is placed over the entire assembly and sealed to the mold (1) by the sealant tape (6). Then, air is sucked out from the vacuum bag (5) for a given period of time, in some instances for hours, causing the resin and other undesirables to be sucked out from the laminate (1). The laminate (1) can then be cured (i.e. heat treated) so as to form the desired structure. The curing technique can consist of maintaining an elevated temperature for a certain period of time so as to enable cross-linking in the resin.
Such a technique is used in numerous fields. In aeronautics, vacuum bagging can be used to create composite materials in the shape of relatively small components, such as a part of a wing, for example. Vacuum bagging can also be used to form composite materials in the shape of relatively large components as well, such as sections of an aircraft fuselage.
U.S. Pat. No. 5,171,510 issued Dec. 15, 1992 to Barquet et al. relates to a method of producing a frame made of a composite material. The method involves draping pre-impregnated fabrics on a form, and placing inflatable bladders between the form and a counter form. A mold is then closed on the form, bladders and the counter form, and the bladders are then inflated to compress the fabrics against the form and counter form.
United States patent application published Oct. 27, 2011 under publication No. US 2011/0259515 A1 and in the name of Rotter et al. relates to a method for forming composite layups having complex geometries. A composite layup is placed on a bag and bladder. The bag and bladder are both inflated to compact the layup against a part surface, and are then deflated so that a tool assembly can be withdrawn.
Also known to the Applicant are the following patents and/or patent applications: U.S. Pat. No. 7,811,495 B2; and EP 2 402 134 A2.
However, a drawback associated with traditional vacuum bagging and other gas-extraction techniques is that they might not be ideal for large composite structures, such as sections of aircraft fuselages, which have large upper surfaces requiring much labour and skill to properly apply a vacuum bag. In these structures, consumable materials can tend to fall off the upper surfaces due to gravity, which renders traditional vacuum bagging techniques more time consuming and resource intensive. Another drawback associated with traditional techniques is that for large composite structures, such as those having large upper surfaces, an important volume of air needs to be vacuumed so as to properly position the vacuum bag, which causes further delays in the composite material preparation process.
It would therefore be advantageous to provide a simpler, more efficient technique of vacuum bagging large structures. It would be advantageous to use a tool to facilitate the application of a vacuum bag prior to, or during, curing of a composite layup. It would also be advantageous if this tool could be reused repeatedly, thereby procuring cost savings.